2001 Corolla Check Engine Light Issue

Hi
I have a toyota corolla 2001, check engine light was was on for last 1-2 months, i need to get PA inspection so i took it to a local mechanic who got code PA0171 , so he changed the O2 sensor, but still the problem is there,
Also my car is now stalling, specially in morning, it does not take any pick up.
Also when i stop the car, it does not take pickup, also it slows when climbing steep hill

HiI have a toyota corolla 2001, check engine light was was on for last 1-2 months, i need to get PA inspection so i took it to a local mechanic who got code PA0171 , so he changed the O2 sensor, but still the problem is there, Also my car is now stalling, specially in morning, it does not take any pick up.Also when i stop the car, it does not take pickup, also it slows when climbing steep hill

What should i do to get it fixed

Ashish

Not sure what a PA0171 code is - but there is a P0171 code. This code refers to a condition of System Too Lean (Bank 1) - usually refers to the upstream O2 sensor or the O2 sensor closest to the engine. What this means is that the oxygen sensor in bank 1 detected a lean condition or too much oxygen in the exhaust.

Note it doesn't mean that the sensor is faulty (though it could be a bad sensor in some cases). Probably 90% of the time, the O2 sensor is fine - but almost every mechanic will replace it (they have to make money some how). On 2000+ Corollas - the most common cause for this code popping up is from a dirty MAF sensor in the airbox.

From the symptoms that you described - it sounds like a dirty MAF sensor and possibly dirty throttle body. As both will contribute to hesitation, poor idling, and poor performance. Sometimes it will lead to reduced fuel economy. I would take a look at the MAF and TB first - cleaning them is minimal in cost and will reveal if any other components may be contributing to this condition (sparkplugs, induction system, ignition, etc.) A good mechanic will always diagnose a condition (from diagnostic codes or visual/audible inspection) and check all common suspect areas and clean or inpect as necessary before replacing a single part. Problem is finding one to do just that - as time is money and it is cheaper and faster to swap parts at the owners expense than properly diagnose the issue. Sounds like you paid for an unnecessary O2 sensor replacement to me, hope that you got the old part back (always a good thing to have and proves that they replaced the part in the first place).

Hi
I just cleaned the MAF sensor and air take maifold, now the pick up and stalling probelm is gone, but i am having a weird problem
I turned off the check engine light and drove for about 80 miles, the light did not come on, but next day i started driving and the check engine came on again after about 7-8 miles.
And the code is same P0171,
I have already changed O2 sensor, do i need to change MAF sensor also??

If the code comes back like you said - could be a faulty MAF sensor. They are fairly delicate pieces - doesn't take much to cause them to go bad. Pricing varys a bit - anywhere from $70 to as much as $175+, depends on where you look.

Also - any air leaks after the MAF sensor could cause problems. Check the vacuum hoses, PCV hose, all connections to the throttle body, make sure the intake pipe running to the TB is in good shape and not ripped anywhere (assuming OEM intake) and makes a good seal. Exhaust leak in the mainfold can also suck in extra air - causing the code to pop up. Check for leaks before the cat - make sure the O2 sensor they installed is on good and tight. I've seen a few cases where they cross-threaded the bung on the exhaust manifold and it rattled free causing erroneous readings.

Also depends on how you cleared the code - pulled the battery connection or cleared it with a scanner. On the 8th gen Corollas - you can do it either way, but to be sure - a scanner will make sure it is truely gone.

I'd check all those areas before I start dropping some cash for parts - once those are exhausted or ruled out - then you might have to bite the bullet and get a new MAF sensor.

Hi
Okay i went to mechanic again and checked the code, now i have 2 codes P0171 and P0420
P0420 is catalyst converter,
So is this caused by MAP sensor? do i need to still change it or the problem is some where else now

Trouble is - you cannot pull the code, look it up and see what needs to be changed - there are diagnostic steps that must be followed or you'll end up just wasting money swapping parts.

A P0420 code is described as - Catalyst System Efficiency Below Threshold (Bank 1). What this means is that the oxygen sensor located after the catalytic converter is detecting that the converter is not working as efficiently as it should be. This would indicate several possible causes:
- O2 sensor is dead or lazy in response
- engine coolant temperature sensor is faulty or has a bad connection
- possible physical damage to exhaust manifold, catalytic converter, or the exhaust pipe
- ignition timing is off (retarded spark timing)
- and a few more

The MAF sensor (your model has MAF "Mass Air Flow" not MAP "Manifold Absolute Pressure" - two completely different systems) could be the cause - but it seems you have a more complicated issue here or that the real problem is masked by these common ones.

Not sure what you meant by "Do i pay for the parts put in by this mechanic?" - if you meant that you may have paid for parts that were not necessary or fixed the problem - hard to say for sure without looking at the car, but I'd say NO given that the same OBD-II codes keep coming back. Hopefully you got the original parts back - they can be tested later to see if they are actually bad or not. None of this will be covered by the factory warranty unless you have additional coverage that states it will be covered - except for possibly the catalytic converter (Federal Emissions coverage protects most parts for 36months/36K miles and "specified major emission control components" for 8years/80K miles).

Seems like the place you took your car to did a diagnostic and changed a part. If that did not fix the problem you brought it in for, then you should be entitled to some kind of refund - incorrect parts or service incorrectly performed.

I have had the same issue with my 01 Corrolla. I replaced my Cat, front and rear O2 sensors, and maf sensor. It ran better for a while, but now the check engine light is back on. My mechanic suggested replacing the front O2 sensor again, because I drove on it for about a year with a bad cat. I brought my car into one place and they said my cat was fine, so I didn't know what to do. I had a problem with a stuck oil ring in my moter and it was burning oil like crazy, which is what screwed up my cat, so I had the motor swapped out. If you change your maf sensor, that is something you can do yourself. I bought mine through Autozone for $75 and it took 2 minutes to change. If that doesn't fix it, it my be your cat or rear sensor. I can post pics of where the maf sensor is if you want. Good luck.

I had a P0171 and P0300 on my 2000 VE (48K miles). The symptoms included rough starting and idling, and decreased power at accelleration. The MAF sensor was visibly dirty. I cleaned it thoroughly with electronics cleaning spray (and cleaned all easily accessible sensor connectors at the same time.) I then reset the ECM with the battery disconnect method. The improvement was instantaneous and complete and has lasted the duration of a 30 mile test drive in varied conditions. If the fix persists it will have been an extremely simple and economical solution. Thanks to all who recommended it. I'll post here if the problem recurs.

I wonder what percentage of engine problems are attributable to dirty sensors of one kind or another (and how much has been spent needlessly replacing parts in these cases.)

I've checked Haynes and P0171 is "fuel injection system lean". So it might be related to your upstream O2 sensor... sure the mechanic changed out the right one? There are two. Also, did he back-probe the existing sensor before he changed it? That would tell you if there was a problem with the sensor at all.

You might have a problem elsewhere like a clogged fuel filter. There are two of them (one in the gas tank, another after). Theoretically, a bad tank of gas could clog the fuel filter... as can leaving the car with a half-tank of gas for months (today's gasoline goes rancid pretty fast!).

I had a P0171 and P0300 on my 2000 VE (48K miles). The symptoms included rough starting and idling, and decreased power at accelleration. The MAF sensor was visibly dirty. I cleaned it thoroughly with electronics cleaning spray (and cleaned all easily accessible sensor connectors at the same time.) I then reset the ECM with the battery disconnect method. The improvement was instantaneous and complete and has lasted the duration of a 30 mile test drive in varied conditions. If the fix persists it will have been an extremely simple and economical solution. Thanks to all who recommended it. I'll post here if the problem recurs.

I wonder what percentage of engine problems are attributable to dirty sensors of one kind or another (and how much has been spent needlessly replacing parts in these cases.)

P0300 is "multiple cylinder misfire". There's a problem with your ignition system. Perhaps one of the coils that feed the spark-plugs is blown out.

Ouroboros, are you responding to me? If so, thanks, but I don't think you read my post very carefully. I said the problem appears to have been fixed by cleaning the MAF sensor. Why then are you suggesting that I replace an oxygen sensor, fuel filter, and/or spark coil--at a potential cost of hundreds of dollars? This is, ironically, exactly the kind of "replace this, replace that" mentality (overlooking the possibility of merely dirty sensors) that I was commenting about. I rest my case.

I had a P0171 and P0300 on my 2000 VE (48K miles). The symptoms included rough starting and idling, and decreased power at accelleration. The MAF sensor was visibly dirty. I cleaned it thoroughly with electronics cleaning spray (and cleaned all easily accessible sensor connectors at the same time.) I then reset the ECM with the battery disconnect method. The improvement was instantaneous and complete and has lasted the duration of a 30 mile test drive in varied conditions. If the fix persists it will have been an extremely simple and economical solution. Thanks to all who recommended it. I'll post here if the problem recurs.

I wonder what percentage of engine problems are attributable to dirty sensors of one kind or another (and how much has been spent needlessly replacing parts in these cases.)

I suspect there are a lot of cases of unnecessary parts being changed,